Petroleomics: Chemistry of the Underworld

Home , Electrospray ionization, Kendrick mass, Petroleomics

Petroleomics: Chemistry of the underworld

Alan G. Marshalla,b,1 and Ryan P. Rodgersa,b,1

aNational High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310-4005; and bDepartment of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306

Edited by Fred W. McLafferty, Cornell University, Ithaca, NY, and approved August 14, 2008 (received for review May 24, 2008)

Each different molecular elemental composition—e.g., CcHhNnOoSs— neutrals. Because many heteroatom-containing components has a different exact mass. With sufficiently high mass resolving (NnOoSs) of petroleum are highly polar, ESI is specific and power (m/⌬m50% Ϸ 400,000, in which m is molecular mass and ⌬m50% especially efficient in generating their gas-phase ions. Although is the mass spectral peak width at half-maximum peak height) and petroleum crude oils typically contain 90% hydrocarbons mass accuracy (<300 ppb) up to Ϸ800 Da, now routinely available (CcHh), the NnOoSs-containing molecules are typically the most from high-field (>9.4 T) Fourier transform ion cyclotron resonance problematic with respect to pollution, fouling of catalysts, for- mass spectrometry, it is possible to resolve and identify uniquely and mation of deposits during production and processing, corrosion, simultaneously each of the thousands of elemental compositions emulsions, and the highest-boiling fractions of lowest economic from the most complex natural organic mixtures, including petroleum value. ESI coupled with low-resolution MS was first applied to crude oil. It is thus possible to separate and sort petroleum compo- petroleum by Zhan and Fenn (6). High-resolution ESI FT-ICR nents according to their heteroatom class (NnOoSs), double bond MS of petroleum has subsequently resolved and identified number of rings plus double bonds involving Ͼ17,000 different elemental compositions for organic bases and ؍ equivalents (DBE carbon, because each ring or double bond results in a loss of two acid in crude oil (7). hydrogen atoms), and carbon number. ‘‘Petroleomics’’ is the charac- Access to many of the remaining 90% of petroleum compo- terization of petroleum at the molecular level. From sufficiently nents is afforded by field desorption/ionization (FD) and atmo- complete characterization of the organic composition of petroleum spheric pressure photoionization (APPI). Continuous-flow FD and its products, it should be possible to correlate (and ultimately FT-ICR MS yields abundant ions from several species not predict) their properties and behavior. Examples include molecular observed by ESI, including benzo- and dibenzothiophenes, mass distribution, distillation profile, characterization of specific frac- furans, cycloalkanes, and polycyclic aromatic hydrocarbons tions without prior extraction or wet chemical separation from the (PAHs) (8). However, FD experiments are slow because of the original bulk material, biodegradation, maturity, water solubility (and need to ramp the current to the FD emitter over a period of a oil:water emulsion behavior), deposits in oil wells and refineries, couple of minutes so as to volatilize/ionize species of successively efficiency and specificity of catalytic hydroprocessing, ‘‘heavy ends’’ increasing boiling point. APPI FT-ICR MS (9) can accumulate (asphaltenes) analysis, corrosion, etc. one mass spectral dataset in a few seconds and is thus better suited for signal averaging of a few hundred scans for increased Fourier transform ͉ ion cyclotron resonance ͉ mass spectrometry ͉ dynamic range. APPI of petroleum requires the ultrahigh reso- petroleum ͉ fossil fuel lution of FT-ICR MS for two reasons: (i) APPI ionizes a broader range of compound classes, and thus the mass spectrum contains he rapidly ballooning interest in characterization of petro- approximately five times as many peaks as an ESI mass spectrum of the same crude oil sample; and (ii) the same analyte molecule Tleum crude oil and its products derives from the confluence ϩ• ϩ ϩ of three recent developments: (i) the rapidly increasing cost of may produce both M and (M H) ions, making it necessary to resolve Mϩ• containing one 13C from (MϩH)ϩ containing all crude oil (up to $120 per barrel at this writing), (ii) the global 12 market shift toward heavier/more acidic/higher sulfur crude oil C, a mass difference of only 4.5 mDa (see below). Laser as the supplies of light ‘‘sweet’’ (low sulfur) crudes are depleted, desorption/ionization mass spectrometry, although highly useful and (iii) the introduction of ultrahigh-resolution mass analysis to for biomolecule analysis, does not provide a reliable represen- separate and identify up to tens of thousands of crude oil tation of petroleum components because of significant aggre- components in a single step. Because the organic composition of gation and fragmentation at the laser power required to generate petroleum is so complex, its characterization was until recently a useful number of gas-phase ions (10). However, recent intro- limited to bulk properties (e.g., density, viscosity, osmotic pres- duction of a two-color laser method (11), in which the first laser sure, light scattering, UV-visible and infrared spectroscopy, desorbs the neutrals and the second laser ionizes them, appears NMR, x-ray scattering, and absorption-edge spectroscopy) and to overcome the disadvantages of single-color laser desorption/ various wet chemical separations based on (e.g.) solubility, ionization. boiling point, gas chromatography, and liquid chromatography. Saturated hydrocarbons are especially problematic, because The historical development of those applications, as well as prior virtually all methods for ionizing neutral saturated hydrocarbons low- and high-resolution mass spectrometry of petroleum, have produce extensive fragmentation, thereby making it hard to been reviewed elsewhere (1). identify the neutral precursors in the original sample as well as Fourier transform ion cyclotron resonance mass spectrometry vitiating quantitation. Recently, laser-induced acoustic desorption (LIAD) of neutrals, followed by chemical ionization with (FT-ICR MS) offers the highest available broadband mass appropriate reagents, has shown great promise in achieving resolution, mass resolving power, and mass accuracy (2). It was first applied to petroleum via electron ionization of petroleum

distillates (3, 4). However, the relatively low magnetic field (3.0 Author contributions: A.G.M. and R.P.R. designed research; R.P.R. performed research; T) limited the m/z range, the need to volatilize the sample limited R.P.R. contributed new reagents/analytic tools; R.P.R. analyzed data; and A.G.M. wrote the the molecular weight range (especially for heteroatom- paper. containing species), and electron ionization produced extensive The authors declare no conﬂict of interest. fragmentation (especially of alkyl chains). This article is a PNAS Direct Submission. Electrospray ionization (ESI) (5) is most efficient for polar 1To whom correspondence may be addressed. E-mail: [email protected] or molecules and typically generates positive ions by protonating [email protected]. (basic) neutrals and negative ions by deprotonating (acidic) © 2008 by The National Academy of Sciences of the USA

18090–18095 ͉ PNAS ͉ November 25, 2008 ͉ vol. 105 ͉ no. 47 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0805069105 Downloaded by guest on September 29, 2021 petroleum mass spectrum (15). Ultrahigh mass accuracy is needed for a different reason. Fig. 1 shows the mass defects (defined in the figure) for the most abundant isotope of each of SPECIAL FEATURE several common chemical elements. Every isotope of every element has a different mass defect. (By definition, the mass defect of 12C is zero.) Thus, if the mass of a molecule can be measured with sufficiently high accuracy (in practice, Ϸ0.0003 Da for molecules up to Ϸ1,000 Da in mass), then its elemental composition can usually be determined uniquely from its mass alone (16, 17). Fig. 2 provides examples of some of the closest mass ‘‘splits’’ encountered in mass spectrometry of petroleum. Two of the most important close doublets are molecules whose 12 32 elemental compositions differ by C3 vs. SH4 (to identify sulfur-containing components, see Fig. 2) and 13C vs. 12C1H (for APPI MS, see above). Results and Discussion Molecular Mass Distribution. The first step in characterization of organics in petroleum is to determine the molecular mass distribution, particularly for ‘‘heavy ends’’ high-boiling components and residues. It is now well established that the average Fig. 1. Atomic mass defects for selected isotopes of some common chemical Ͻ elements. Because no two have the same mass defect, it is possible to deter- molecular mass of asphaltenes is 1,000 Da (18). Higher average mine a unique elemental composition for any molecule from a sufﬁciently molecular masses inferred from prior vapor-phase osmometry accurate mass measurement. and size-exclusion chromatography may be attributed to forma- tion of noncovalent aggregates because of too-high concentration and/or use of solvents that promote aggregation. Aggre- efficient (and uniformly efficient) ionization of saturated hy- gation has been demonstrated by mass-selective isolation of

drocarbons over a wide molecular mass range (12, 13). singly charged dimer ions in the range 840–860 Da, followed by CHEMISTRY ‘‘Petroleomics’’ is the principle that from sufficiently complete collisional activation at collision energies too low to break characterization of the organic composition of petroleum and its covalent bonds. The heterodimers dissociate to yield a distribu- relatives and products, it should be possible to correlate (and tion of monomeric ions, and those ions do not dissociate when ultimately predict) their properties and behavior (7, 14). In this subjected to the same collision conditions (1). In this way, article, we describe the basis for extraction of elemental com- aggregates up to tetramers have been demonstrated. Moreover, positions from sufficiently accurate mass measurements and the abundance of dimers relative to monomers increases with present various methods to sort the thousands of resulting increasing sample concentration—additional evidence for non- chemical formulas in chemically and practically important ways. covalent complexes.

Mass Defects: The Key to Unlocking Chemical Formulas Elemental Composition Assignment from Accurate Mass Measure- Ultrahigh mass resolving power (m/⌬m50% Ն 400,000) up to ment. Once the thousands of peaks in an FT-ICR mass spectrum Ϸ800 Da is needed to resolve the thousands of peaks in a of a petroleum sample have been resolved and converted from

Fig. 2. Positive-ion electrospray 9.4-T FT-ICR mass spectrum of a European crude oil, containing Ϸ8,000 resolved and identiﬁed peaks. Several of the mass splits commonly encountered in crude oil are shown in the mass-scale-expanded 300-mDa Inset. Data were provided by A. M. McKenna.

Marshall and Rodgers PNAS ͉ November 25, 2008 ͉ vol. 105 ͉ no. 47 ͉ 18091 Downloaded by guest on September 29, 2021 ion cyclotron frequency to mass, the next step is to assign each mass to a unique elemental composition. Even with ultrahigh mass resolving power (e.g., m/⌬m50% ϭ 400,000 up to 800 Da), such assignments may not be possible based on mass measurement alone. Fortunately, petroleum and its derivatives typically consist primarily of homologous series. Each homologous series is categorized by heteroatom class (NnOoSs), double bond equivalents (DBE) (see Eq. 1), and carbon number. The DBE is equal to the number of rings plus double bonds involving carbon (19): ϭ Ϫ ϩ ϩ Double bond equivalents (CcHhNnOoSs) c h/2 n/2 1. [1] Within each heteroatom class, many DBE values are possible. For example, C42H59N1 belongs to the N1 class with DBE ϭ 14, whereas C42H53N1 belongs to the same heteroatom class, N1, but its DBE is 17. DBE thus affords a direct measure of aromaticity of petroleum components. [In the petroleum industry, a more common index is the ‘‘hydrogen deficiency,’’ Z, defined from the Fig. 3. Sorting of compounds based on their elemental compositions. (Bot- elemental composition, CcH2cϩZ. We prefer DBE, because a tom) Heteroatom class (all species with the same NnOoSs composition). (Mid- saturated hydrocarbon with zero rings or double bonds has a dle) Distribution of DBE (double bond equivalents ϭ rings plus double bonds Ϫ DBE of 0 but a Z-value of 2. In any case, it is easy to convert to carbon) distribution for members of the O2 heteroatom class. (Top) Carbon between the two: Z ϭϪ2(DBE) ϩ n ϩ 2, in which n is the number distribution for O2 species with DBE ϭ 2. Graphical combinations of number of nitrogens in the chemical formula.] these distributions furnish characteristic images of various petroleum Consider a homologous series of molecules of the same materials. heteroatom class and DBE, but a varying degree of alkylation. Members of that series will vary in composition by multiples of DBE vs. carbon number for a given heteroatom class. For -CH2, corresponding to multiples in mass of 14.0565 Da. A particularly useful way to identify such a series is to convert the Syste`me example, Fig. 4 shows such a plot for a distillation cut from international d’unite´s (SI) mass to ‘‘Kendrick’’ mass (20): Athabasca bitumen. Interestingly, the O2 class (presumably carboxylic acids) are not aromatic because their DBE values are Kendrick mass ϭ SI mass ϫ (14.00000/14.0565). [2] typically 4 or less (and the simplest aromatic carboxylic acid would have DBE ϭ 5). Plots of DBE vs. carbon number have Thus, successive members of an alkylation series (i.e., same proved especially useful in characterizing hydrotreatment in heteroatom class and same number of rings plus double bonds petroleum processing (22–24), vacuum gas oil distillation cuts involving carbon) will differ by 14.00000 in Kendrick mass and (25), water-soluble acids and bases (26), saturates vs. aromatics will therefore each have the same Kendrick mass defect: (27), heat exchanger deposits (28), oil:water emulsion interfacial material (29–31), (lack of) matrix effects in saturates/aromatics/ Kendrick mass defect ϭ nominal Kendrick mass resins/asphaltenes (SARA) (32) fractionation (33), naphthenic Ϫ Kendrick mass, [3] acids (1, 34, 35), sulfur-containing polycyclic aromatics (27, 36–38), distillates (39, 40), and other applications discussed in in which nominal Kendrick mass is the Kendrick mass rounded this article. to the nearest integer. Another graphical compositional image is a ‘‘van Krevelen’’ plot, Members of a given alkylation series are thereby readily identified. Because elemental compositions can be assigned with high confidence for the lower mass members of each series, the assignments can be extended to 800–1,000 Da by extrapolation. That procedure was the key to ‘‘cracking’’ the problem of mass assignments for petroleum components (21).

Compositional Sorting: Graphical Images Derived from Heteroatom Class, DBE, and Carbon Number. Having proceeded from thousands of ICR frequencies to thousands of accurate masses to thousands of elemental compositions, the next issue is how to represent those compositions in convenient graphical form rather than in a table with thousands of entries. In fact, the elemental composition yields three independent properties of a molecule: heteroatom class (NnOoSs), double bond equivalents, and number of carbons (for a given class and DBE, the carbon number is a measure of the degree of alkylation). Those properties may be sorted hierarchically, as shown in Fig. 3. First, compositions are sorted according to heteroatom class. For a given heteroatom class (in this case, O2, typically consisting mainly of carboxylic acids), there is a distribution of DBE values. Finally, for a given class (in this case, O2) and Fig. 4. Plots of double bond equivalents (DBE) vs. carbon number for the DBE (in this case, 2), one can display the carbon distribution. 375–400°C distillation cut from the negative-ion ESI 9.4 T FT-ICR mass spec- Among the various possible graphical images derived from trum of Athabasca bitumen (1 mg/ml) in toluene/methanol, spiked with 2% elemental compositions, we find that the most useful is a plot of (by volume) ammonium hydroxide. Data were provided by D. F. Smith.

18092 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0805069105 Marshall and Rodgers Downloaded by guest on September 29, 2021 SPECIAL FEATURE

Fig. 6. Plot of double bond equivalents vs. carbon number for all monoisotopic CcHhS1 members of the petroleome database, compiled from dozens of positive- and negative-ion ESI and APPI FT-ICR mass spectra. The diagonal line represents the maximum possible DBE for each carbon number. The entries are not abundance-weighted; i.e., each different elemental composition is shown by a single dot. Data were provided by I. Stroe and J. E. Velasquez.

nitrogen rings can be found and identified in a single (positive- ion) mass spectrum, whereas ESI requires separate positive- and Fig. 5. van Krevelen plot of H/C ratio vs. S/C ratio for all sulfur-containing ions negative-ion mass spectra to reach the same result. in an APPI positive-ion 9.4 T FT-ICR mass spectrum of an Asian light crude oil. Ͻ Ͻ To avoid overlap between Sx classes, only ions with 300 m/z 750 are The Petroleome. We have, to date, resolved and identified included. Data were provided by A. M. McKenna. Ͼ60,000 distinct elemental monoisotopic elemental composi- 12 1 14 16 32 tions, Cc Hh Nn Oo Ss, from ions in positive- and negative-

ion ESI and APPI FT-ICR mass spectra of dozens of petroleum CHEMISTRY typically of H/C ratio vs. O/C ratio. The van Krevelen plot (like 13 15 34 Kendrick mass) was originally devised to represent bulk elemental crude oil samples. [Species with one or more C, N, S, etc. compositions (41). The advent of ultrahigh-resolution FT-ICR MS are not counted separately because they are chemically essen- tially identical. Moreover, a neutral composition based on made it possible to extend both of those ideas to distinguish all of ϩ• ϩ ϩ the individual elemental compositions simultaneously. The van observation of both M and (M H) ions is counted only Krevelen plot was initially applied to dissolved organic matter (42), once.] Fig. 6 is a distribution of DBE vs. carbon number for just and later to petroleum (43, 44) and coal (45). van Krevelen plots the CcHhS1 members of the ‘‘petroleome.’’ The diagonal line have been used to characterize, e.g., asphaltene vs. its parent oil represents the maximum possible DBE for each carbon number (46), biodegradation (14), and crude oil vs. its deposit (47). Fig. 5 in a planar polycyclic aromatic molecule. Interestingly, over the is a van Krevelen plot for an Asian light crude oil but plotted here tens of millions of years during which petroleum is formed, as H/C ratio vs. S/C ratio. The van Krevelen plot nicely separates virtually all possible combinations of DBE and carbon number Ϸ Ϸ the sulfur classes (S1, S2, and S3, each of which would require a are generated up to DBE 25 and carbon number 40, and, Ϸ separate plot of DBE vs. carbon number) on the abscissa, and the with decreasing aromaticity, up to carbon number 80. Similar ordinate provides a measure of unsaturation. (Note that lower H/C trends are found for other heteroatom classes. ratio corresponds to higher DBE.) As the petroleome database expands, we envision several uses, by analogy to proteomic and other such databases. First, once the Nitrogen Speciation. For an APPI FT-ICR mass spectrum, addi- database is sufficiently complete, it should be possible to search tional information emerges if DBE in Eq. 1 is calculated from the only among its members (rather than all chemically possible elemental composition of the ion rather than its precursor elemental compositions), thereby simplifying and speeding the neutral in the original sample. Thus, odd-electron radical cations assignment of a unique elemental composition to each mass have integer DBE values (because loss of an electron does not spectral peak. Second, once the monoisotopic species have been affect the DBE calculated from Eq. 1), whereas protonated or identified, one can search for the same species containing one or deprotonated (even-electron) ions have half-integer DBE values more 13C, 15N, and/or 34S in place of 12C, 14N, 32S to improve the (because changing the number of hydrogens by one changes reliability of the original assignment. Third, by including addi- DBE by Ϯ0.5 in Eq. 1). That property makes it possible to tional descriptors, it becomes possible to characterize crude oils distinguish five-membered from six-membered nitrogen ring (and their processed products) with respect to geographic origin species as follows (48). (e.g., for oil spills), density, total acid number (milligrams of KOH The primary ionization pathways for aromatic N1 class com- to neutralize1gofsample), corrosivity, tendency to form sodium pounds (acridine, with nitrogen in a six-membered pyridine ring, or calcium naphthenate deposits, emulsions, distillation profiles and carbazole, with nitrogen in a five-membered pyrrolic ring) sorted by heteroatom compound class, fractions separated by by APPI (positive-ion) and ESI (negative-ion and positive-ion) solubility and/or chromatographic elution [e.g., saturates/ differ. Proton transfer yields even-electron [MϩH]ϩ or [MϪH]Ϫ aromatics/resins/asphaltenes, SARA (32)], etc. Finally, similar da- ions with half-integer calculated DBE values. Positive-ion APPI tabases may be compiled and exploited for coal (49), biofuels, can also form odd-electron radical cations with integer DBE humic (50) and fulvic (51) acids, dissolved organic matter (52–54), values. Thus, from elemental compositions derived from APPI and other complex organic mixtures. FT-ICR MS, it is possible to distinguish between heterocyclic It is important to recognize that the present analysis is limited nitrogen species in six-membered rings [positive-ion ESI (half- to compositional possibilities. For many elemental compositions, integer ion DBE value)] or APPI (half-integer ion DBE value) there can be multiple isomers (e.g., positional isomers, such as from five-membered nitrogen ring species [negative-ion ESI butane vs. isobutane; alcohol vs. ketone, stereoisomers, etc.). (half-integer ion DBE value)] or positive-ion APPI (integer ion Additional (typically spectroscopic) information is needed to DBE value). APPI is more convenient because both types of distinguish some of those possibilities. For example, the number

Marshall and Rodgers PNAS ͉ November 25, 2008 ͉ vol. 105 ͉ no. 47 ͉ 18093 Downloaded by guest on September 29, 2021 of isomers for the single elemental composition, C14H10,is5.3ϫ Materials and Methods 106 (55)! Petroleum samples were typically dissolved at 100 mg/mL in toluene. Two The biggest remaining problem for mass-based petroleomics serial dilutions yielded a 2 mg/mL solution that may be further diluted in is quantitation. No single ionization method produces ions from toluene to 0.5 mg/mL for APPI analysis and 1 mg/mL in toluene:methanol (1:1 different analyte neutrals with equal efficiency. For example, vol/vol) for ESI analysis. Conditions for microelectrospray (1) and APPI (9) analyses are described elsewhere. Our FT-ICR mass spectra were acquired with ESI typically generates positive ions by protonation (of basic 56 57 analytes) and negative ions by deprotonation (of acidic analytes). custom-built 9.4 T and 14.5 T instruments. Multiple (100–200) time-domain acquisitions were averaged for each sample, Hanning-apodized, and zero- Because ESI is typically achieved by addition of a weak acid (e.g., ﬁlled once before fast Fourier transform and magnitude calculation. The formic acid) or weak base (e.g., ammonium hydroxide), the quadrupolar electric trapping potential approximation (58) converted ICR species accessible by ESI are typically limited to relatively strong frequency to mass-to-charge ratio. Instrument control, data acquisition, and acids (e.g., carboxylic acids) or relatively strong bases (e.g., data analysis were handled by a modular ICR data station.§ Negative ion data pyridinic nitrogen). Thus, ESI is ‘‘blind’’ to aromatic hydrocar- were collected with similar parameters and appropriate polarity changes. bons, thiophenes, furans, etc. Efforts are currently underway to Petroleum ions were typically singly charged, based on the unit m/z separation 12 13 12 extend the range of acidity/basicity for ESI. For example, between Cn and C1 Cn-1 isotopic variants of the same elemental compo- incubation of petroleum with methyl iodide can result in meth- sition (59). FT-ICR mass spectra were internally calibrated with respect to a homologous series of ions present in high abundance in each sample. Masses ylation of benzo- and dibenzothiophenes and their alkylated for singly charged ions with relative abundance of Ͼ6␴ of baseline rms noise congeners, thereby producing positive ions in solution for high were exported to a spreadsheet. Measured masses were then converted from yield from positive-ion electrospray (37). Unfortunately, the the SI mass scale to the Kendrick mass scale for identiﬁcation of homologous reaction is slow (overnight), and its efficiency diminishes with series. Kendrick mass defect analysis was used for peak assignments as de- increasing molecular mass. Much more uniform ionization ef- scribed above (21). ficiency across widely different functional groups is currently provided by field desorption or atmospheric pressure photoionization, as noted above. §Blakney GT, Hendrickson CL, Marshall AG, Improved data acquisition system for Fourier At this writing, petroleomics has been the subject of two transform ion cyclotron resonance mass spectrometry, 55th American Society for Mass review articles (7, 14), one monograph (47), two petroleomics Spectrometry Annual Conference on Mass Spectrometry, June 3–7, 2007, Indianapolis, IN, symposia (Petroleomics: The Next Grand Challenge for Chemical MPD067 (abstr). Analysis, PittCon 2003, Orlando, FL, March, 2003; Symp. VI. Petroleomics: From Petroleum Composition to Commercial Real- ACKNOWLEDGMENTS. We thank the various coauthors in our listed refer- ity, II. International Applied Statistical Physics Molecular En- ences, as well as Priyanka Juyal, Brandie M. Ehrmann, Amy M. McKenna, gineering Conference, Puerto Vallarta, Mexico, August, 2003), Mmilili Mapolelo, Jade E. Velasquez, Brian S. Bingham, and Ioana Stroe. This work was supported by the National Science Foundation National High Field and 65 journal publications. Petroleomics is rapidly taking its Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Facility (Grant place as the most comprehensive tool for characterization of DMR-06-54118), Florida State University, and the National High Magnetic crude oil and its derivatives. Field Laboratory.

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trospray ionization and field desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry. Energy Fuels 18:1424–1428. SPECIAL FEATURE resonance mass spectrometry. Energy Fuels 21:973–981. 46. Klein GC, Kim S, Rodgers RP, Marshall AG, Yen A (2006) Mass spectral analysis of 31. Stanford LA, et al. (2007) Detailed elemental compositions of emulsion interfacial asphaltenes. II. Detailed compositional comparison of asphaltenes deposit to its crude material vs. parent oil for nine geographically distinct light, medium, and heavy crude oil counterpart for two geographically different crude oils by electrospray ionization oils, detected by negative- and positive-ion electrospray ionization Fourier transform Fourier transform ion cyclotron resonance mass spectrometry. Energy Fuels 20:1973– ion cyclotron resonance mass spectrometry. Energy Fuels 21:963–972. 1979. 32. Rudzinski WE, Aminabhavi TM, Sassman S, Watkins LM (2000) Isolation and charac- 47. Rodgers RP, Marshall AG (2006) Chapter 3: Petroleomics: Advanced Characterization terization of the saturate and aromatic fractions of a Maya crude oil. Energy Fuels of Petroleum Derived Materials by Fourier Transform Ion Cyclotron Resonance Mass 14:839–844. Spectrometry (FT-ICR MS). Asphaltenes, heavy oils and petroleomics, eds Mullins OC, 33. Klein GC, Angstro¨m A, Rodgers RP, Marshall AG (2006) Use of saturates/aromatics/ Sheu EY, Hammami A, Marshall AG (Springer, New York), pp 63–93. resins/asphaltenes (SARA) fractionation to determine matrix effects in crude oil anal- 48. Purcell JM, Rodgers RP, Hendrickson CL, Marshall AG (2007) Speciation of nitrogen ysis by electrospray ionization Fourier transform ion cyclotron resonance mass spec- containing aromatics by atmospheric pressure photoionization or electrospray ioniza- trometry. Energy Fuels 20:668–672. tion Fourier transform ion cyclotron resonance mass spectrometry. J Am Soc Mass 34. Barrow MP, Headley JV, Peru KM, Derrick PJ (2004) Fourier transform ion cyclotron Spectrom 18:1265–1273. resonance mass spectrometry of principal components in oilsands naphthenic acids. 49. Wu Z, Jernstro¨m S, Hughey CA, Rodgers RP, Marshall AG (2003) Resolution of 10,000 J Chromatogr A 2058:51–59. compositionally distinct components in polar coal extracts by negative-ion electros- 35. Headley JV, Peru KM (2007) Characterization of naphthenic acids from Athabasca oil pray ionization Fourier transform ion cyclotron resonance mass spectrometry. Energy sands using electrospray ionization: The significant influence of solvents. Anal Chem Fuels 17:946–953. 79:6222–6229. 50. Stenson AC, Landing WM, Marshall AG, Cooper WT (2002) Ionization and fragmenta- 36. Rodgers RP, Andersen KV, White FM, Hendrickson CL, Marshall AG (1998) Resolution, tion of humic substances in electrospray ionization Fourier transform ion cyclotron elemental composition, and simultaneous monitoring by Fourier transform ion cyclo- resonance mass spectrometry. Anal Chem 74:4397–4409. tron resonance mass spectrometry of organosulfur species before and after diesel fuel 51. Stenson AC, Marshall AG, Cooper WT (2003) Exact masses and chemical formulas of processing. Anal Chem 70:4743–4750. individual Suwannee River fulvic acids from ultrahigh resolution electrospray ioniza- 37. Mu¨ller H, Andersson JT, Schrader W (2005) Characterization of high-molecular-weight tion Fourier transform ion cyclotron resonance mass spectra. Anal Chem 75:1275–1284. sulfur-containing aromatics in vacuum residues using Fourier transform ion cyclotron 52. Tremblay LB, Dittmar T, Marshall AG, Cooper WJ, Cooper WT (2007) Molecular char- resonance mass spectrometry. Anal Chem 77:2536–2543. acterization of dissolved organic matter in a north Brazilian mangrove porewater and 38. Panda SK, Schrader W, Al-Hajji A, Andersson JT (2007) Distribution of polycyclic mangrove-fringed estuary by ultrahigh resolution Fourier transform-ion cyclotron aromatic sulfur heterocycles in three Saudi Arabian crude oils as determined by Fourier resonance mass spectrometry and excitation/emission spectroscopy. Mar Chem transform ion cyclotron resonance mass spectrometry. Energy Fuels 21:1071–1077. 105:15–29. 39. Pakarinen JMH, Tera¨va¨ inen MJ, Pirskanen A, Wickstro¨m K, Vainiotalo P (2007) A 53. Kujawinski EB, Behn M (2006) Automated analysis of electrospray ionization Fourier positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass transform ion cyclotron resonance mass spectra of natural organic matter. Anal Chem

spectrometry study of Russian and North Sea crude oils and their six distillation 78:4363–4373. CHEMISTRY fractions. Energy Fuels 21:3369–3374. 54. Hertkorn N, et al. (2007) An integrated NMR and FTCIR mass spectroscopic study to 40. Tera¨va¨ inen MJ, Pakarinen JMH, Wickstro¨m K, Vainiotalo P (2007) Comparison of the characterize a new and major refractory component of (marine) natural organic composition of Russian and North Sea crude oils and their eight distillation fractions matter (NOM) at the molecular level, CRAM: Carboxyl-rich alicyclic molecules. Geochim studied by negative-ion electrospray ionization Fourier transform ion cyclotron reso- Cosmochim Acta 71:A399–A399. nance mass spectrometry: The effect of suppression. Energy Fuels 21:266–273. 55. Hertkorn N, et al. (2007) High-precision frequency measurements: Indispensable tools 41. van Krevelen DW (1950) Graphical-statistical method for the study of structure and at the core of the molecular-level analysis of complex systems. Anal Bioanal Chem reaction processes of coal. Fuel 29:269–284. 389:1311–1327. 42. Kim S, Kramer RW, Hatcher PG (2003) Graphical method for analysis of ultrahigh- 56. Senko MW, Hendrickson CL, Emmett MR, Shi SDH, Marshall AG (1997) External accu- resolution broadband mass spectra of natural organic matter, the Van Krevelen mulation of ions for enhanced electrospray ionization Fourier transform ion cyclotron diagram. Anal Chem 75:5336–5344. resonance mass spectrometry. J Am Soc Mass Spectrom 8:970–976. 43. Wu Z, Strohm JJ, Song C, Rodgers RP, Marshall AG (2005) Comparative compositional 57. Schaub TM, et al. (2008) High-performance mass spectrometry: Fourier transform ion analysis of untreated and hydrotreated oil by electrospray ionization Fourier trans- cyclotron resonance at 14.5 tesla. Anal Chem 80:3985–3990. form ion cyclotron resonance mass spectrometry. Energy Fuels 19:1072–1077. 58. Ledford EB, Jr, Rempel DL, Gross ML (1984) Space charge effects in Fourier transform 44. Kim S, et al. (2005) Microbial alteration of the acidic and neutral polar NSO compounds mass spectrometry. Mass calibration. Anal Chem 56:2744–2748. in petroleum revealed by Fourier transform ion cyclotron resonance mass spectrome- 59. Senko MW, Beu SC, McLafferty FW (1995) Automated assignment of charge states from try. Org Geochem 36:1117–1134. resolved isotopic peaks for multiply charged ions. J Am Soc Mass Spectrom 6:52–56.

Marshall and Rodgers PNAS ͉ November 25, 2008 ͉ vol. 105 ͉ no. 47 ͉ 18095 Downloaded by guest on September 29, 2021